Membrane gas extractor

ABSTRACT

An improved gas/liquid separator cell utilizing membranes formed of coherent films of unsintered polytetrafluorethylene.

United States Patent [191 Mousseau, Jr. et al.

1451 May 29,1973

Strand ..55/158 Pfafferle .155/ l 6 Dounoucos ..55/ 16 Jaconelli ..55/16Chesnut et aL. ..252/12 Klein ..55/16 Primary ExaminerCharles N. HartAttorney-Meyer Neishloss, Deane E. Keith and Wil- ABSTRACT An improvedgas/liquid separator cell utilizing membranes formed of coherent filmsof unsintered 8 Claims, 7 Drawing Figures [54] MEMBRANE GAS EXTRACTOR3,342,729 9/1967 [75] Inventors: Richard J. Mousseau, Jr.; HomerPatnode, both of Gibsoma, Pa. 3,520,803 7/1970 [73] Assignee: GulfResearch 8: Development Com- 3,002,770 10/1961 pany, Pittsburgh, Pa. 83/ 1972 [22] Filed: June 9, 1971 [21] Appl. No.: 151,212

liam Kovensky 52 US. Cl ..55/158 [57] [51] Int. Cl. ..B0ld 59/12 [58]Field of Search ..55/16,158, 159; 210/321 polytetrafluorethylene. [56]References Cited UNITED STATES PATENTS 3/1966 Huffman etal ..55/16MEMBRANE GAS EXTRACTOR This invention relates to the art of fluidseparation. More in particular, the invention pertains to an improvedmeans to measure gases dissolved in liquids utilizing membraneseparation.

The invention was developed in the environment of geophysicalexploration, and in that particular area thereof wherein it is desiredto take samples from a body of water, and to then analyze for any gaseswhich may be dissolved in the water. The theory is that hydrocarbondeposits in the bed underlying the body of water will often evidencethemselves by gas seeps, and that by analyzing for hydrocarbon gases inthe water such deposits can be found. As is known to those skilled inexploration, the raw data concerning dissolved gases must then becorrelated to navigation data, currents, background gases in the water,and the like, before identifying a likely place to drill a hydrocarbonwell. The invention could have utility in other fields than geophysicalexploration, for example, oceanography, and water pollution studies.

The invention resides in the combination of a particular configurationof a separator cell together with a particular membrane at which thegas/liquid separation occurs. Gas/liquid separation using membranes isgenerally known in the art. In developing the invention many differentmaterials were tried, and all but one were found lacking in one respector another. The membrane must be hydrophobic, i.e., it must repel water,while at the same time permitting the gas molecules to pass through themembrane. The general mechanism and the physics of membrane separationis explained further in the A.C.S. Monograph series text entitledDiffusion and Membrane Technology", by S. B. Tuwiner, published byReinhold in New York, copyright 1962, see particularly the introduction,pages 1-6. However, the particular membrane used in the invention mayfunction as a non-selective porous barrier, rather than by the moreusual processes of solution and diffusion into and through the membrane.The difference in these two mechanisms is well known, and is clearlyshown on page 3 of a brochure number GEA- 8685A 2-70, issued by GeneralElectric Co., Medical Division. In addition to passing the gas freelyand none of the liquid water, the membrane utilized must separate outthe gas at a rate of speed sufficient to permit meaningful results. Someof the membranes which were unsuccessfully used are polyethylene andnonporous Teflon. These materials did function, but at an unacceptablyslow rate of speed.

We have discovered that a certain commercially available tape isuniquely suited for use in the invention. The tape is described in U.S.Pat. No. 3,002,770 to Chesnut et al. From said patent it can be seenthat this material comprises pure Teflon prepared in a certain manner,and intended to be used as pipe dope in tape form. The patent describesthe tape as a coherent film of unsintered polytet rafluoroethylene. Thetape is commercially available from Chemplast Inc. of Wayne, NJ. underthe tradename Chemfluor Lab- Tape. The same material is thought to beavailable under the tradename PIPE-PAC from the Johns- Manville Co. Thetape is thought to be porous as to gas but sufficiently hydrophobic asto prohibit passage of liquid water.

The separator cell of the invention is characterized by its compactconstruction and means to support four membranes therein in two pairsand means to efficiently and quickly supply sample water to the outsideof all membranes and to collect the separated gases from between themembranes of each pair while at the same time holding the membranesapart. The unique plastic tape used as the membrane is quite inexpensiveand the invention provides simple means to disassemble the cell toreplace the tape as needed. The cell parts are of simple construction,while at the same time providing a leak-proof, highly reliablestructure, which is simple to manufacture and yet sure and accurate inuse.

The above and other advantages of the invention will be pointed out orwill become evident in the following detailed description and claims,and in the accompanying drawing also forming a part of the disclosure,in which:

FIG. 1 is a top plan view of a separator cell embodying the invention;

FIG. 2 is a side elevational view thereof;

FIG. 3 is a longitudinal cross-sectional view taken on line 3-3 of FIG.1; and

FIGS. 4, 5, 6 and 7 are cross-sectional views taken on lines 44, 55,6-6, and 7-7 of FIG. 2, respectively.

Referring now to FIGS. 1 and 2, there is shown a separator cell 10embodying the invention in general external view. Cell 10 comprises atop member 12, a middle member 14 and a bottom member 16 all securedtogether by a plurality of bolts or screws 18. Between the top andmiddle members 12 and 14 is a screen assembly 20, and another screenassembly 22 is positioned between the middle and bottom members. Fourmembranes 24, 26, 28 and 30 complete the assembly and are positioned oneto each side of each screen assembly 20 and 22.

The thickness of the plastic tapes is shown greatly exaggerated for thepurpose of clarity in the drawings.

Means are provided to flow a carrier gas between the two sandwiches"formed by each screen assembly 20 and 22 and its two associatedmembranes. To this end, a conduit 32 is connected to top member 12, anda conduit 34 is connected to bottom member 16. A system of internalpassageways, described further below, interconnects the two conduits 32and 34 via the screens in the assemblies 20 and 22.

Means are also provided to flow water or other liquid containingdissolved gases to the outsides of each of the two sandwiches formed byeach screen and its associated two membranes. To this end, a series ofthree conduits 36, 38 and 4 9 supply sample water to each of the top,middle and bottom members, and flow said water across the outside of allof the four membranes via other internal passageways described below.

Three conduits 42, 44 and 46 are connected to each of the top, middleand bottom members to carry away the sample liquid, and are associatedeach with one of three supply conduits 36, 38 and 40, respectively. Ofcourse, as will be evident to those skilled in the art, each set of thethree supply or the three removal con-. duits could be connectedtogether by suitable fittings somewhere spaced away from the separatorcell 10, or three separate supply systems could be provided for betteroperation and control.

Referring now to FIG. 3, the structure of the two screen assemblies 20and 22 is shown in detail. The two screens are identical inconstruction, and therefore only screen 20 will be described in detail.As is obvious, the screens are mounted in the assembly upsidedown withrespect to each other. Each screen assembly comprises a central framingmember 48 within which is snugly fitted the screen 50 itself. Means areprovided to snugly hold the screen 50in position within the framingmember 48. To this end, screen assembly 20 comprises a pair of screenhold-down plates 52 and 54. Thus, the screen 50 is held in the assemblyby its snug fit within frame 48 and by the hold-down plates 52 and 54which grip the edges of the screen above and below. As is clear, theframing member 48 has a thickness substantially equal to or slightlygreater than the thickness of screen 50.

The three members 52, 54 and 48 are securely fastened together by anysuitable means such as soldering or cementing, and these members, aswell as screws 18, are made from suitable corrosion resistant materialsuch as brass. Similarly, screen 50 is made of a corrosion resistantmaterial such as stainless steel. In order to provide a large degree ofmechanical support for the membranes 24, 26, 28 and 30, screen 50 ispreferably of fine mesh. In the successfully constructed embodiment,screen 50 was formed of stainless steel wire, 0.0075 inches diameter,having a mesh of 60.

The exaggeration of the membranes is particularly evident in FIG. 3. Infact, the membranes are thinner than the hold-down plates 52 and 54. Thecommercial tapes used in the invention are available on the market inonly certain widths. In order to maximize the surface area of membranewhich is operative, the cell was designed to use the maximum availablewidth, which dimension sets the minimum distance between a pair ofopposing screws 18. Lengthwise, as shown in FIG. 3, the tape is used inpieces equal to or larger than the overall length of cell 10, andsuitable openings are formed in the tape for the gas passageways, asdescribed below.

A single continuous gas passageway through cell is provided by openingsand slots in the screen assemblies cooperating with suitable passagewaysformed in the main members 12, 14 and 16. The carrier gas, which may beair or helium or some other gas depending upon the nature of the gasesto be recovered, is supplied via conduit 32 through a passageway 56formed in top member 12, a suitable clearance opening in membrane 24, anopening 58 formed in hold-down plate 52, and then a passageway 60 formedin framing member 48, to thereby impinge upon one end of the screen 50.Referring to FIG. 7, it can be seen that passageway 60 is of keyholeconfiguration. The carrier gas then proceeds through the screen 50 fromend to end between the two associated membranes 24 and 26 picking up thegases which permeate through the membranes from the sample water on theopposite sides of the membranes. At the left side of FIG. 3 the carriergas enters another passageway 62, similar to passageway 60, passesthrough an opening 64 in plate 54 (similar to opening 58 in plate 52),passes through a clearance opening in the membrane 26, and then througha passageway 66 formed in center member 14. As mentioned above, the twoscreen assemblies and 22 are identical, and thus the pathway for thecarrier gas through screen assembly 22 is provided in a similar manner,finally terminating at a passageway 68 in bottom member 16 whichcommunicates with conduit 34.

Conduit 34 delivers the collected gases to any conventional analyticalmeans, such as a gas chromatograph.

Referring now to FIGS. 3 and 5 in particular, there is shown the meansto flow the gas containing water into one side of the sample cell, outalong the length of the membranes, across the four membranes, and thenout of the cell. Top member 12 is formed with a pair of elongatedarcuate grooves each communicating with one of the conduits 36 and 42which flow gas containing sample water through the top member 12. Member12 is formed with passageways 36a and 42a which are in effectcontinuations of their associated conduits 36 and 42. In a similarmanner, bottom member 16 is formed with a pair of grooves 72interconnecting the passageways 40a and 46a. The center member 14 isformed with four grooves 74 each two of which form a clear flow pathwaytop to bottom, i.e., between the two membranes 26 and 28. The shape andlocation of the elongated grooves 70, 72 and 74 are instrumental infully utilizing the membranes in that they spread the water out alongthe length of the tape and then flow it across the tape.

In operation, the water is supplied to the separator cell 10 under apressure slightly greater than the pressure of the carrier gas, wherebythe membranes are positioned against the screens as shown in FIG. 5 inparticular, so that the gas containing water can flow over the outsidesurface of the membranes. The gases permeate the membranes untilcompositional equilibrium is obtained across the membranes. For thisreason, relatively large amounts of sample water are flowed forrelatively small amounts of carrier gas.

As an indication of orders of magnitude and to enrich the teaching, butnot as a limitation, a sample cell in accordance with the invention hasbeen built and successfully used, and this device measured about 10inches long, about 1% inches high and about 2 inches wide, was madeentirely of brass and stainless steel, as described above, and utilizedthe plastic tape described which had a width of about 1 inch and athickness of about 0.004 inches. In use, for example, sample water couldbe flowed at about 2 gal/min at a pressure of about 25 psi, and carriergas at about 2 cc/min at atmospheric pressure.

While the invention has been described in detail above, it is to beunderstood that this detailed description is by way of example only, andthe protection granted is to be limited only within the spirit of theinvention and the scope of the following claims.

We claim:

1. A gas/liquid separation cell comprising a top member, a bottom memberand a middle member therebe tween, a first screen assembly positionedbetween said top member and said middle member, a second screen assemblypositioned between said middle member and said bottom member, agas/liquid separation membrane positioned to each side of each of saidscreen assemblies, whereby four such membranes are provided; means toremovably secure all of said top, middle and bottom members, said twoscreen assemblies, and said four membranes together; means to flowliquid containing dissolved gases to the side of each of said membranesopposite said screen through said top, middle and bottom members acrossthe outsides of said membranes, and thence away from said membranes; andmeans to flow carrier gas through said two screen assemblies serially,whereby dissolved gases in said fluid pass through said membranes andare picked up by said flow of carrier gas through said screens.

2. The combination of claim 1, each of said membranes consisting of acoherent film of unsintered polytetrafluoroethylene.

3. The combination of claim 1, each of said screen assemblies comprisinga central framing member adapted to snugly receive a screen, saidframing member in said screen having substantially equal thicknesses,said screen assemblies further comprising upper and lower hold-downplates, means to secure said holddown plates to said framing member, andsaid holddown plates being slightly larger than said framing member togrip the edges of said screen therebetween.

4. The combination of claim 3, said framing member and said hold-downplates consisting of brass, and said screen consisting of stainlesssteel having a wire size of 0.0075 and a mesh size of 60.

5. The combination of claim 3, said first and second screen assembliesbeing of identical construction and disposed insaid separator cell inupside-down relationship to each other.

6. The combination of claim 5, said carrier gas flow means comprisingregistering passageways formed in said upper, middle and lower membersand registering passageways formed in said screen assemblies, wherebysaid carrier gas flows through portions of said passageways in one ofsaid upper and lower members, through said passageway in said firstscreen assembly through said screen in said first screen assembly fromend to end thereof, through a passageway in the opposite end of saidframing member, through the portions of said passageway in said middlemember, through the similar structure in said second screen assembly,and out said passageway in the other of said upper and lower mainmembers.

7. The combination of claim 1, said screen assemblies and said membranesbeing of elongated configuration, said means to flow said gas containingliquid comprising at least two elongated slots formed in each of saidupper, middle and lower members, said slots being positioned to theopposite sides of said elongated membranes, whereby said liquid suppliedto one side of said cell flows into said elongated slot and across theentire operative face of the associated membrane and then out the otherslot.

8. In apparatus for separating gas out of a liquid in which the gas isdissolved by passing the gas laden liquid over a membrane to accomplishsuch separation, the improvement comprising making the membrane of acoherent film of unsintered polytetrafluoroethylene, whereby the gaspasses through the porous film and the liquid is repelled by the film,said apparatus comprising a pair of elongated members, screen meansbetween said members, an elongated membrane to each side of said screenmeans, means to flow liquid containing dissolved gases to one elongatedside of each of said membranes and then across the outsides of saidmembranes and then away from said membranes, and means to flow carriergas through said screen means.

2. The combination of claim 1, each of said membranes consisting of acoherent film of unsintered polytetrafluoroethylene.
 3. The combinationof claim 1, each of said screen assemblies comprising a central framingmember adapted to snugly receive a screen, said framing member in saidscreen having substantially equal thicknesses, said screen assembliesfurther comprising upper and lower hold-down plates, means to securesaid hold-down plates to said framing member, and said hold-down platesbeing slightly larger than said framing member to grip the edges of saidscreen therebetween.
 4. The combination of claim 3, said framing memberand said hold-down plates consisting of brass, and said screenconsisting of stainless steel having a wire size of 0.0075 and a meshsize of
 60. 5. The combination of claim 3, said first and second screenassemblies being of identical construction and disposed in saidseparator cell in upside-down relationship to each other.
 6. Thecombination of claim 5, said carrier gas flow means comprisingregistering passageways formed in said upper, middle and lower membersand registering passageways formed in said screen assemblies, wherebysaid carrier gas flows through portions of said passageways in one ofsaid upper and lower members, thRough said passageway in said firstscreen assembly through said screen in said first screen assembly fromend to end thereof, through a passageway in the opposite end of saidframing member, through the portions of said passageway in said middlemember, through the similar structure in said second screen assembly,and out said passageway in the other of said upper and lower mainmembers.
 7. The combination of claim 1, said screen assemblies and saidmembranes being of elongated configuration, said means to flow said gascontaining liquid comprising at least two elongated slots formed in eachof said upper, middle and lower members, said slots being positioned tothe opposite sides of said elongated membranes, whereby said liquidsupplied to one side of said cell flows into said elongated slot andacross the entire operative face of the associated membrane and then outthe other slot.
 8. In apparatus for separating gas out of a liquid inwhich the gas is dissolved by passing the gas laden liquid over amembrane to accomplish such separation, the improvement comprisingmaking the membrane of a coherent film of unsinteredpolytetrafluoroethylene, whereby the gas passes through the porous filmand the liquid is repelled by the film, said apparatus comprising a pairof elongated members, screen means between said members, an elongatedmembrane to each side of said screen means, means to flow liquidcontaining dissolved gases to one elongated side of each of saidmembranes and then across the outsides of said membranes and then awayfrom said membranes, and means to flow carrier gas through said screenmeans.